基于DEM-CFD的混流式水轮机粗沙水流条件泥沙磨损机制研究

Sediment Erosion Mechanism of Francis Hydro-turbine under Coarse Sand Water Flow Conditions Based on DEM-CFD

摘要:

含沙水流条件下水轮机内部泥沙颗粒与湍流两相介质相互作用对水轮机壁面冲蚀磨损机制有重要影响。基于GPU加速耦合颗粒离散元与计算流体力学方法求解混流式水轮机内部颗粒-流体系统。通过泥沙颗粒真实外形建模，DEM-CFD耦合模拟获得水轮机泥沙颗粒流磨损特性。结果表明：GPU加速可节省计算成本，粗沙水流下泥沙颗粒受水流影响在尾水管内小开度工况以“短螺旋”方式运动，而大开度工况则以“长螺旋”方式运动；小开度工况球形多面体泥沙颗粒曳力最大值比球体颗粒大34.78%。大开度工况颗粒对活动导叶的碰撞强度比固定导叶大74.13%，说明其冲击磨损强于固定导叶；粒子对固定导叶的滑动距离平均最大值比活动导叶大21.43%，说明其剪切磨损强于活动导叶。活动导叶、转轮叶片和尾水管壁面磨损情况与文献试验结果及电站实际磨损一致；在汛期控制水轮机在小开度工况运行是有利的。研究结果可为改善水轮机泥沙磨损破坏提供理论参考。

Abstract:

The interaction between sediment particles and turbulent two-phase media inside hydro-turbine under sand containing water flow conditions has a significant impact on the erosion and wear mechanism of the turbine wall. Based on GPU accelerated coupled particle discrete element (DEM) and computational fluid dynamics (CFD) methods to solve the internal particle fluid system of hydro-turbine, the wear characteristics of sediment particle flow in hydro-turbine through DEM-CFD coupling simulation were obtained by using the real shape modeling of sediment particles. The results showed that GPU acceleration can save computational costs. Sediment particles under coarse sand flow were affected by the water flow and moved in a “short spiral” manner in the draft tube at small opening case, while at big opening case, they moved in a “long spiral” manner. The maximum resistance of spherical polyhedral sediment particles at small opening case was 34.78% higher than that of spherical particles. The collision strength of particles on the guide vanes at big opening case was 74.13% higher than that of the stay vanes, indicating that their impact wear was stronger than that of the stay vanes. The average maximum sliding distance of particles on the stay vanes was 21.43% higher than that of the guide vanes, indicating that their shear wear was stronger than that of the guide vanes. The wear of the guide vanes, runner blades and draft tube walls was consistent with the experimental results in the literature and the actual wear of the power plant. It was beneficial to control the operating case of the hydro-turbine during the flood season and operate it at small opening case. The research result can provide theoretical reference for improving the sediment erosion and damage of hydro-turbine.